The invention relates to polyurethane and polyisocyanurate closed-cell foams. More particularly, the invention relates to the addition of xcex1-methyl styrene, isobutanol and/or isopropanol to reduce vapor pressure, improve k-factor, enhance the solubility of the blowing agent in the premix and/or improve the processing characteristics of polyurethane and polyisocyanurate closed-cell foams prepared with a blowing agent comprising a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134) and mixtures thereof.
The class of foams known as low density rigid polyurethane or polyisocyanurate foam has utility in a wide variety of insulation applications including roofing systems, building panels, refrigerators and freezers. The methods of producing polyurethane and polyisocyanurate foams are generally known and consist in general of the reaction of an organic polyisocyanate and a polyol or mixture of polyols in the presence of a volatile blowing agent, which is caused to vaporize by the heat liberated during the reaction of isocyanate or isocyanurate and polyol. This reaction can be enhanced through the use of amine and/or other catalysts as well as surfactants. The catalysts ensure adequate curing of the foam, while the surfactants regulate and control cell size.
The foam industry has historically used liquid fluorocarbon blowing agents such as trichlorofluoromethane (CFC-11) and 1,1-dichloro-1-fluoroethane (HCFC-141b) because of their ease of use in processing conditions. Fluorocarbons act not only as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are the major contributor to the low thermal conductivity properties of rigid urethane foams. The escape of certain fluorocarbons, most notably chlorofluorocarbons, to the atmosphere is now recognized as potentially contributing to the depletion of the stratospheric ozone layer and to global warming. In view of the environmental concerns with respect to chlorofluorocarbon blowing agents, it is now generally accepted that it would be more desirable to use hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) rather than the chlorofluorocarbons. Exemplary hydrofluorocarbons suitable for use as blowing agents in the preparation of polyurethane and polyisocyanurate foams are 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane and 1,1,2,2-tetrafluoroethane (known in the art as HFC-245fa, HFC-134a, and HFC-134, respectively). These materials, however, possess a lower boiling point and a correspondingly higher vapor pressure than the prior art materials. This difference becomes significant when any of HFC-245fa, HFC-134a or HFC-134 are incorporated into the B-side of a foam formulation that is either transported in or used directly from a low pressure rated container.
The use of a fluorocarbon as the preferred commercial expansion or blowing agent in insulating foam applications is based in part on the resulting k-factor associated with the foam produced. K-factor is defined as the rate of transfer of heat energy by conduction through one square foot of one inch thick homogenous material in one hour where there is a difference of one degree Fahrenheit perpendicularly across the two surfaces of the material. As is generally known in the art, the cell gas composition of the foam at the moment of manufacture does not necessarily correspond to the equilibrium gas composition after aging or sustained use. The gas in a closed cell foam frequently exhibits compositional changes as the foam ages leading to such known phenomena as increase in thermal conductivity or loss of insulation value (both measured in terms of k-factor) and thermal aging. Since the utility of closed-cell polyurethane-type foams is based, in part, upon their thermal insulation properties, it would be advantageous to identify materials which lower the k-factor of foams and reduce thermal aging of the foams over time.
Methods for improving the k-factor and/or thermal aging characteristics of polyurethane foam are disclosed in U.S. Pat. Nos. 5,696,306 and 5,837,742. There remains a need in the art for polyurethane and polyisocyanurate foams prepared from a blowing agent comprising a hydrofluorocarbon selected from the group consisting of HFC-245fa, HFC-134a, HFC-134 and mixtures thereof, which foams have improved processibility, k-factor and/or thermal aging characteristics. The instant invention meets this need by providing additives that reduce the vapor pressure of HFC-245fa and HFC-134a and/or reduce the k-factor of foams produced from blowing agents comprising these hydrofluorocarbons.
It has now been discovered that the addition of one or more of xcex1-methyl styrene, isobutanol and isopropanol to the B-side of a polyurethane or polyisocyanuate foam formulation comprising a blowing agent comprising a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and mixtures thereof results in reduced vapor pressure, improved k-factor, enhanced solubility of the blowing agent and/or improved processing characteristics of the foams. The addition of xcex1-methyl styrene to the foam formulation results in improved thermal conductivity (k-factor) and thermal aging characteristics. With respect to thermal conductivity, the term xe2x80x9cimprovedxe2x80x9d refers to a decrease in the k-factor of the foam.
Accordingly, the invention relates to a method of preparing polyurethane and polyisocyanurate foam compositions comprising the step of reacting and foaming a mixture of ingredients which react to form polyurethane or polyisocyanurate foams in the presence of a blowing agent comprising a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and mixtures thereof and an effective amount of an additive selected from the group consisting of xcex1-methyl styrene, isobutanol, isopropanol and mixtures thereof, preferably from about 0.02 to about 10 weight percent of said additive, based on the amount of blowing agent. In another embodiment, the invention provides a method of preparing polyurethane and polyisocyanurate foam compositions comprising the step of reacting and foaming a mixture of ingredients which react to form polyurethane or polyisocyanurate foams in the presence of a blowing agent comprising 1,1,1,3,3-pentafluoropropane and xcex1-methyl styrene, preferably from about 0.02 to about 5 weight percent xcex1-methyl styrene, based on the amount of blowing agent.
The invention further relates to a closed cell foam prepared from a polymer foam formulation containing as a blowing agent a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and mixtures thereof and an effective amount of an additive selected from the group consisting of xcex1-methyl styrene, isobutanol, isopropanol and mixtures thereof, preferably from about 0.02 to about 10 weight percent of said additive, based on the amount of blowing agent. In one embodiment, the invention provides a closed cell foam prepared from a polymer foam formulation containing a blowing agent comprising 1,1,1,3,3-pentafluoropropane and xcex1-methyl styrene, preferably from about 0.02 to about 5 weight percent xcex1-methyl styrene, based on the amount of blowing agent.
In another embodiment, the invention provides a closed cell foam containing a cell gas comprising a blowing agent comprising a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and mixtures thereof and an additive selected from the group consisting of xcex1-methyl styrene, isobutanol, isopropanol and mixtures thereof, preferably from about 0.02 to about 10 weight percent of said additive, based on the amount of blowing agent. In one embodiment, the invention provides a closed cell foam containing a cell gas comprising a blowing agent comprising 1,1,1,3,3-pentafluoropropane and xcex1-methyl styrene, preferably from about 0.02 to about 5 weight percent xcex1-methyl styrene, based on the amount of blowing agent.
The invention further relates to a blowing agent composition comprising a hydrofluorocarbon selected from the group consisting of 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane and mixtures thereof and an additive selected from the group consisting xcex1-methyl styrene, isobutanol, isopropanol and mixtures thereof, preferably from about 0.02 to about 10 weight percent of said additive, based on the amount of blowing agent. In one embodiment, the invention provides a blowing agent composition 1,1,1,3,3-pentafluoropropane and xcex1-methyl styrene, preferably from about 0.02 to about 5 weight percent xcex1-methyl styrene, based on the amount of blowing agent.
As used herein, an effective amount of additive means an amount, based on the amount of blowing agent, which reduces the vapor pressure of a foam formulation B-side to below the vapor pressure of the corresponding foam prepared in the absence of additive. Generally, an effective amount is from about 0.02 to about 10 weight percent, based on the amount of blowing agent. The xcex1-methyl styrene is preferably added in an amount of from about 0.5 to about 2 weight percent, based on the amount of blowing agent.
As used herein, blowing agent composition refers to HFC-245fa or HFC-134a singly or in combination with other non-ozone depleting blowing agents, such as, for example, other hydrofluorocarbons, e.g., difluoromethane (HFC-32), difluoroethane (HFC-152), trifluoroethane (HFC-143), tetrafluoroethane (HFC-134), pentafluoropropane (HFC-245), hexafluoropropane (HFC-236), heptafluoropropane (HFC-227); C4-C7 hydrocarbons, including but not limited to butane, isobutane, n-pentane, isopentane, cyclopentane, hexane and isohexane; inert gases, e.g., air, nitrogen, carbon dioxide; and water in an amount of from about 0.5 to about 2 parts per 100 parts of polyol. Where isomerism is possible for the hydrofluorocarbons mentioned above, the respective isomers may be used either singly or in the form of a mixture.
HFC-245fa is a known material and can be prepared by methods known in the art such as those disclosed in WO 94/14736, WO 94/29251, WO 94/29252 and U.S. Pat. No. 5,574,192. Difluoroethane, trifluoroethane, tetrafluoroethane, heptafluoropropane and hexafluoropropane are available for purchase from AlliedSignal Inc. of Morristown, N.J. The xcex1-methyl styrene, isobutanol and isopropanol components of the invention are also commercially available.
With respect to the preparation of rigid or flexible polyurethane or polyisocyanurate foams using a blowing agent comprising 1,1,1,3,3-pentafluoropropane or 1,1,1,2-tetrafluoroethane, any of the methods well known in the art can be employed. See Saunders and Frisch, Volumes I and II Polyurethanes Chemistry and Technology (1962). In general, polyurethane or polyisocyanurate foams are prepared by combining under suitable conditions an isocyanate (or isocyanurate), a polyol or mixture of polyols, a blowing agent or mixture of blowing agents, and other materials such as catalysts, surfactants, and optionally, flame retardants, colorants, or other additives.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended foam formulations. Most typically, the foam formulation is pre-blended into two components. The isocyanate or polyisocyanate composition comprises the first component, commonly referred to as the xe2x80x9cAxe2x80x9d component or xe2x80x9cA-side.xe2x80x9d The polyol or polyol mixture, surfactant, catalysts, blowing agents, flame retardant, water and other isocyanate reactive components comprise the second component, commonly referred to as the xe2x80x9cBxe2x80x9d component or xe2x80x9cB-sidexe2x80x9d. While the surfactant and fluorocarbon blowing agent are usually placed on the polyol side, they may be placed on either side, or partly on one side and partly on the other side. Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A and B side components either by hand mix, for small preparations, or preferably machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like. Optionally, other ingredients such as fire retardants, colorants, auxiliary blowing agents, water and even other polyols can be added as a third stream to the mix head or reaction site. Most conveniently, however, they are all incorporated into one B component.
The xcex1-methylstyrene, isobutanol and isopropanol additives of the present invention may be added to B-side of the foam formulation, or to the blowing agent per se, by any manner well known in the art.
Any organic polyisocyanate can be employed in polyurethane or polyisocyanurate foam synthesis inclusive of aliphatic and aromatic polyisocyanates. Preferred as a class are the aromatic polyisocyanates. Preferred polyisocyanates for rigid polyurethane or polyisocyanurate foam synthesis are the polymethylene polyphenyl isocyanates, particularly the mixtures containing from about 30 to about 85 percent by weight of methylenebis(phenyl isocyanate) with the remainder of the mixture comprising the polymethylene polyphenyl polyisocyanates of functionality higher than 2. Preferred polyisocyanates for flexible polyurethane foam synthesis are toluene diisocyanates including, without limitation, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and mixtures thereof
Typical polyols used in the manufacture of rigid polyurethane foams include, but are not limited to, aromatic amino-based polyether polyols such as those based on mixtures of 2,4- and 2,6-toluenediamine condensed with ethylene oxide and/or propylene oxide. These polyols find utility in pour-in-place molded foams. Another example is aromatic alkylamino-based polyether polyols such as those based on ethoxylated and/or propoxylated aminoethylated nonylphenol derivatives. These polyols generally find utility in spray applied polyurethane foams. Another example is sucrose-based polyols such as those based on sucrose derivatives and/or mixtures of sucrose and glycerine derivatives condensed with ethylene oxide and/or propylene oxide. These polyols generally find utility in pour-in-place molded foams.
Typical polyols used in the manufacture of flexible polyurethane foams include, but are not limited to, those based on glycerol, ethylene glycol, trimethylolpropane, ethylene diamine, pentaerythritol, and the like condensed with ethylene oxide, propylene oxide, butylene oxide, and the like. These are generally referred to as xe2x80x9cpolyether polyolsxe2x80x9d. Another example is the graft copolymer polyols which include, but are not limited to, conventional polyether polyols with vinyl polymer grafted the polyether polyol chain. Yet another example is polyurea modified polyols which consist of conventional polyether polyols with polyurea particles dispersed in the polyol.
Examples of polyols used in polyurethane modified polyisocyanurate foams include, but are not limited to, aromatic polyester polyols such as those based on complex mixtures of phthalate-type or terephthalate-type esters formed from polyols such as ethylene glycol, diethylene glycol, or propylene glycol. These polyols are used in rigid laminated boardstock, and may be blended with other types of polyols such as sucrose based polyols, and used in polyurethane foam applications.
Catalysts used in the manufacture of polyurethane foams are typically tertiary amines including, but not limited to, N-alkylmorpholines, N-alkylalkanolamines, N,N-dialkylcyclohexylamines, and alkylamines where the alkyl groups are methyl, ethyl, propyl, butyl and the like and isomeric forms thereof, as well as heterocyclic amines. Typical, but not limiting, examples are triethylenediamine, tetramethylethylenediamine, bis(2-dimethylaminoethyl)ether, triethylamine, tripropylamine, tributylamine, triamylamine, pyridine, quinoline, dimethylpiperazine, piperazine, N,N-dimethylcyclohexylamine, N-ethylmorpholine, 2-methylpiperazine, N,N-dimethylethanolamine, tetramethylpropanediamine, methyltriethylenediamine, and mixtures thereof.
Optionally, non-amine polyurethane catalysts are used. Typical of such catalysts are organometallic compounds of lead, tin, titanium, antimony, cobalt, aluminum, mercury, zinc, nickel, copper, manganese, zirconium, and mixtures thereof. Exemplary catalysts include, without limitation, lead 2-ethylhexoate, lead benzoate, ferric chloride, antimony trichloride, and antimony glycolate. A preferred organo-tin class includes the stannous salts of carboxylic acids such as stannous octoate, stannous 2-ethylhexoate, stannous laurate, and the like, as well as dialkyl tin salts of carboxylic acids such as dibutyl tin diacetate, dibutyl tin dilaurate, dioctyl tin diacetate, and the like.
In the preparation of polyisocyanurate foams, trimerization catalysts are used for the purpose of converting the blends in conjunction with excess A component to polyisocyanurate-polyurethane foams. The trimerization catalysts employed can be any catalyst known to one skilled in the art including, but not limited to, glycine salts and tertiary amine trimerization catalysts, alkali metal carboxylic acid salts, and mixtures thereof. Preferred species within the classes are potassium acetate, potassium octoate, and N-(2-hydroxy-5-nonylphenol)methyl-N-methylglycinate.
Also included in the mixture are blowing agents or blowing agent blends. Generally speaking, the amount of blowing agent present in the blended mixture is dictated by the desired foam densities of the final polyurethane or polyisocyanurate foams products. The polyurethane foams produced can vary in density, for example, from about 0.5 pound per cubic foot to about 40 pounds per cubic foot, preferably from about 1 to about 20 pounds per cubic foot, and most preferably from about 1 to about 6 pounds per cubic foot. The density obtained is a function of how much of the blowing agent, or blowing agent mixture, is present in the A and/or B components, or that is added at the time the foam is prepared. The proportions in parts by weight of the total blowing agent or blowing agent blend can fall within the range of from 1 to about 60 parts of blowing agent per 100 parts of polyol. Preferably from about 10 to about 35 parts by weight of blowing agent per 100 parts by weight of polyol are used.
Dispersing agents, cell stabilizers, and surfactants may be incorporated into the blowing agent mixture. Surfactants, better known as silicone oils, are added to serve as cell stabilizers. Some representative materials are sold under the names of DC-193, B-8404, and L-5340 which are, generally, polysiloxane polyoxyalkylene block co-polymers such as those disclosed in U.S. Pat. Nos. 2,834,748, 2,917,480, and 2,846,458.
Other optional additives for the blowing agent mixture may include flame retardants such as tris(2-chloroethyl)phosphate, tris(2-chloropropyl)phosphate, tris(2,3-dibromopropyl)phosphate, tris(1,3-dichloropropyl)phosphate, diammonium phosphate, various halogenated aromatic compounds, antimony oxide, aluminum trihydrate, polyvinyl chloride, and the like.